They live a good life! You bought a couple of less than perfect birds, possibly they'll have slightly compromised immune systems??? IMHO you're giving them the chance to enjoy life as chickens.
As Wryop Rock asked How long did they exhibit symptoms before they died?
If you were able to observe this it might help you with the detective work that goes into figuring these things out. Also, were they in an area with new plants growing? I don't know the enviro of your locale but it could be the season for a new plant or pest to come out or maybe some spraying was done or a new product brought onto the property that they have not yet learned to avoid? Sorry, no answers just questions!
As Wryop Rock asked How long did they exhibit symptoms before they died?
If you were able to observe this it might help you with the detective work that goes into figuring these things out. Also, were they in an area with new plants growing? I don't know the enviro of your locale but it could be the season for a new plant or pest to come out or maybe some spraying was done or a new product brought onto the property that they have not yet learned to avoid? Sorry, no answers just questions!